In recent years, various skin adhesive type external preparations such as poultices, tapes and the like have been developed as percutaneous absorption preparations for use in the administration of drugs into the living body through the skin surface. Among them, tapes that contain drugs capable of exerting systemic pharmacological actions are particularly worthy of notice.
Under such actual circumstances, tape type percutaneous absorption preparations have been proposed, developed and partly put into practical use, in which nitroglycerin, isosorbide dinitrate or other drug selected from various steroids, non-steroidal drugs, anesthetic agents, antihypertensive drugs and the like is included in the pressure-sensitive adhesive layer as a pharmacologically active substance. These percutaneous absorption preparations comprises an acrylic or synthetic rubber pressure-sensitive adhesive and a drug for percutaneous absorption mixed therein, and by only placing these percutaneous absorption preparations on the skin surface, the drug is continuously absorbed in a body through the skin surface, thereby providing excellent pharmacological actions.
However, since these preparations are those to be adhered to the skin surface, they have a possibility of causing an eruption on the adhered area of the skin due to irritation and the like when used for a prolonged period of time. That is, the conventional percutaneous absorption preparation generally has a pressure-sensitive adhesive having relatively strong adhesive property or is entirely overcoated with a pressure-sensitive adhesive sheet having strong adhesive property and fixed to the skin through the adhesive property of the sheet, in order to fix the preparation to the skin area securely. When skin adhesion is increased in such a manner, transfer of a drug contained therein to skin (skin transfer) will be improved in general, but there is a possibility that corneous cells on the skin surface applied are damaged on peeling the preparation to remove, and significant skin irritation is caused when the preparation is continuously used for a prolonged period of time repeatedly exchanging it with fresh ones.
For the purpose of reducing such strong adhesion-induced skin irritation, a so-called gel percutaneous absorption preparation has been proposed for example in JP-A-3-220120 (the term "JP-A" as used herein means an "unexamined published Japanese patent application"). This preparation, of which an acrylic pressure-sensitive adhesive layer contains a relatively large amount of oily liquid components having high compatibility so as to impart a soft feeling of touch to the pressure-sensitive adhesive layer, is an epoch-making percutaneous absorption preparation which can reduce skin irritation during its application to the skin due to the soft pressure-sensitive adhesive layer and can be removed smoothly after its use without causing damage to the stratum corneum.
However, since these adhesive type percutaneous absorption preparations are used by adhering them to the skin surface, it is necessary to maintain a balance of their skin adhesion and skin irritation, while simultaneously exerting proper transfer to skin and percutaneous absorption of a drug contained therein. It therefore is an ultimate future object to develop a percutaneous absorption preparation which can satisfy all of these necessities.
The aforementioned preparation of JP-A-3-220120 can exert excellent effects which cannot be found in other conventional percutaneous absorption preparations, but it still has room for improvement in terms of its skin adhesion. In addition, it is desirable to make the size (area) of each percutaneous absorption preparation as small as possible in order to reduce skin irritation, but this preparation also has room for improvement in terms of securing skin adhesion when its area is minimized, as well as skin transfer and percutaneous absorption of drugs.